In 1999, I had finally purchased my first home on about 3.5 acres in the sand hills east of Havana, Illinois. I always thought that if I ever became rooted, I would begin a long-term ecological study of one place in an attempt to gain insight into how and why changes occur in nature, especially within bird communities, over time. For my long-term bird study I chose to work with Project FeederWatch through the Cornell Laboratory of Ornithology. I made this decision because this project has a proven track record, beginning in 1987, with widespread participation; in 2009-2010, for example, there were 15,699 participants in the U.S. and Canada with 407 in Illinois. Also, I wanted my data to be used by ornithologists at the Cornell Lab who conduct a variety of analyses on overwintering birds that are drawn to feeders.
During a FeederWatch season, the observer counts birds at one or more feeders every other week for two consecutive days from November to April. Only the highest number of each species seen at any one time is actually recorded. As an illustration, if five American goldfinches were at the feeder, then later only two goldfinches were at the feeder, only five would be recorded on the data sheet, not seven. There may actually have been seven individuals in the area, or the latter two could have been left over from the original five. We cannot know for sure. But what we do know for sure is that there were at least five present. This conservative method of counting prevents over counting; but, of course, it does not prevent under counting. In addition to birds, the observer records temperature, type of precipitation, habitat information (e.g., number of shrubs and trees present), plus an estimate of the time spent watching the feeder station. The observer need not sit in front of the window all day long, but may watch for any length of time that is convenient. I typically spend anywhere from one to eight hours watching over each two-day count period, glancing out the window more often than not while I am reading or playing the guitar; rarely do I actually sit and watch the feeder for an extended period, unless an interesting behavior is occurring. After each count period, the data are entered into the Cornell FeederWatch database via the Internet.
When I first moved into my new home in the fall of 1999, the surrounding lands on my property were only slightly bird friendly. There were several large trees near the house and dense trees and shrubs around the perimeter of the acreage; but most of the land was a closely mowed lawn, with little wildlife cover. Only American robins and a few other species prefer this type of habitat. Birds had to fly over wide expanses of open area to reach the feeders near my windows from the cover that they found along the edge of the property and further away in the rural countryside with abundant woods and fields. But after a few years of only a minimal amount of mowing, trees and shrubs began to grow near the feeders, soon providing better bird habitat in terms of cover from predators (hawks) and branches for perching near the feeders.
Although I could tell that a variety of changes in the bird community were occurring from year to year, a much clearer picture emerged after I had examined and summarized ten year’s worth of data. One factor that was immediately clear was that a large percentage of the total number of birds coming to my feeders was from non-native species. In the early years, the house sparrow was the most dominant species. Over the years, counts of house sparrows gradually declined, from an average of 16.6 per two-day count in 2000-2001 to 2.6 per two-day count in 2009-2010. During the same time period, counts of house finches increased from an average of 0.6 per two-day count in 2000-2001 to a high of 29.0 in 2005-2006, and then declined to 11.3 in 2009-2010; and counts of Eurasian tree sparrows increased from an average of 8.7 per two-day count in 2000-2001 to a high of 29.1 in 2006-2007, declining to 9.1 in 2009-2010. All of these species are highly competitive with each other, and it may be that the greater numbers of Eurasian tree sparrows, which actually seem to be more aggressive than house sparrows, and house finches out-competed the house sparrows. At any rate, the percentage of individuals from non-native species began at 43.2% in 2000-2001, increased to a high of 65.5% in 2003-2004, and then gradually declined to an all-time low of 31.7% in 2009-2010. This is a good trend, which is undoubtedly related to the decline in house sparrows, but also may be related to the increase in habitat diversity surrounding the feeders. Interestingly, the U.S. Geological Survey’s Breeding Bird Survey for Illinois from 1966 to 2006 also indicates that Illinois’ population of house sparrows has declined and Eurasian tree sparrows and house finches have increased. So the trends at my feeders may also be related to what has happened at a statewide scale. In any case, in 2000-2001, in terms of the average number of individuals counted at my feeders per two-day period, the top five species in order were the house sparrow (#1), American goldfinch, Eurasian tree sparrow, dark-eyed junco, and common grackle. In 2009-2010, the American goldfinch was number one, followed by dark-eyed junco and house finch both tied for second place, Eurasian tree sparrow, northern cardinal, and common grackle.
[Click on the following graphs to enlarge.]
HOFI = House Finch, HOSP = House Sparrow, EUTR = Eurasian Tree Sparrow
The number of non-native species at my feeders remained steady at four (house sparrow, Eurasian tree sparrow, house finch, European starling) until 2008-2009 when the Eurasian collared dove appeared (one individual on only one of ten two-day counts). I had been expecting this for several years because the state’s Eurasian collared dove population has expanded dramatically in recent years. The yearly cumulative number of species (i.e., additive from year to year) coming to the feeders, though, steadily increased from 21 in 2000-2001 to 41 in 2009-2010. The average number of species seen per two-day count also increased from 12.2 in 2000-2001 to a high of 18.6 in 2008-2009, dropping slightly to 17.3 in 2009-2010. This latter trend is likely related to habitat diversity gradually becoming more favorable over the ten-year period as trees and shrubs have replaced a mowed lawn. On the other hand, a complicating factor in this conclusion is that as I have become more interested in doing the counts, I have increased my efforts at observation by spending more time watching at the window. And with all else being equal, more time observing should yield more species, habitat changes notwithstanding. Finally, one would expect that as the years progress, new species will turn up from time to time merely by chance alone.
While counting birds certainly has its rewards, closely watching bird behavior has yielded insights into the species themselves, as a few examples may illustrate. The gregarious non-native species are the most aggressive, and they dominate the feeders when they show up as a group. But they eventually leave the feeders for periods of time, allowing access by less aggressive species. The black-capped chickadee, tufted titmouse, and white breasted nuthatch, I refer to as in-and-out feeders; they can show up at any time, even when numerous house finches and Eurasian tree sparrows are present, quickly grab a single seed, and then fly to a nearby branch or tree with their prize. American goldfinches are the most patient of species, calmly perching on the feeders, eating one seed at a time, especially when the house finches and Eurasian tree sparrows are elsewhere.
Certain species, though, rarely obtain their seeds directly from the hanging feeders, though based on their body types (sparrow-like) they would seem to be perfectly capable of doing so. Rather, they glean their seeds from the ground below the feeders, from seeds that have spilled mainly due to the sloppy Eurasian tree sparrows. Included in this category are the dark-eyed junco, white-crowned sparrow, white-throated sparrow, song sparrow, fox sparrow, and American tree sparrow. Though all of these ground-gleaners have a similar body shape, each species has a characteristic feeding style, and each can usually be identified just by noting subtle differences in each species’ movements. For example, a white-crowned sparrow’s forward ground scratch with both feet is uniquely different from the way any other of a number of species perform the same task. So even with forty or so house finches and Eurasian tree sparrows dominating the ground below the feeder, it is not at all difficult to pick out a single individual of a different species.
Though all species scatter for cover when a sharp-shinned hawk or Cooper’s hawk flies over the feeder area, which is actually a rarity, the blue jay is usually shown the most "respect." When a blue jay arrives on the scene, most species move out of the way. When several calling jays appear together, they quickly gain dominance, but only for a short time, before other species gradually return to join the jays. And with all of this activity around them, woodpeckers, not surprisingly, mostly focus on the suet feeders.
In addition to the seemingly endless variety of bird behaviors on display, the possibility of seeing a rare species is a major factor that helped keep me focused on looking out the window more often than not. A single yellow-bellied sapsucker, for example, showed up on only one occasion in ten years. On December 25-26, 2008, a brown creeper landed on a hackberry tree near the feeders; the tree had not been there eight years before. And pine siskins and purple finches, though certainly not considered rare species, have shown up at the feeders so few times that I become quite excited when either species finally makes another appearance. The occasional accipiter hawk or American kestral may sometimes even perch on top of the feeder stand; and, of course, at such times, no other birds will be found nearby. When these predators appear, the advantages of flocking as a defense mechanism become quite clear, for picking out and following any single individual in the maelstrom of panicking song birds must be a daunting task.
Large flocks of common grackles with a few red-winged blackbirds and brown-headed cowbirds typically begin showing up sometime in March, officially signaling the beginning of the spring season and the coming end of another FeederWatch season. This is a period of transition, when I will look back at the winter’s data and make comparisons to other years, noting if certain trends have continued or been upset by an outlier, such as the 34 American robins that unexpectedly appeared on February 7-8, 2009. And I’ll think about what I have learned about bird behavior and habitat needs. As another FeederWatch season draws to a close, I’ll look forward to the next year and speculate upon what changes I might expect in the coming years. Will house sparrows rebound and reassert their dominance? What new species will show up next year? Or will next year be the first year without new species? What changes will occur in my personal life and on the world stage during the next ten years, I can only guess. Though there are many unknowns, one certainty is that I am committed to this project, and I am looking forward to compiling data summaries every ten years for as long as that is possible.
Project FeederWatch website at http://www.birds.cornell.edu/pfw/ accessed on 23 September 2010.
Sauer, J. R., J. E. Hines, and J. Fallon. 2007. The North American Breeding Bird Survey, Results and Analysis 1966 - 2006. Version 10.13.2007. USGS Patuxent Wildlife Research Center, Laurel, MD.
[NOTE: This posting also appeared in the Winter 2010-2011issue of Illinois Audubon magazine, pages 21-24.]